The present invention relates to a method and apparatus for glossing developer sheets. The developer sheet useful in the present invention can be used in conjunction with conventional pressure-sensitive copy paper or photosensitive imaging systems employing microcapsules to provide visible images upon contact with a color precursor which is imagewise released from the microcapsules and transferred to the developer sheet.
Photosensitive imaging systems employing microencapsulated radiation sensitive compositions are the subject of U.S. Pat. Nos. 4,399,209 and 4,416,966, both of which are hereby incorporated by reference. These imaging systems are characterized in that an imaging sheet including a layer of microcapsules containing a photosensitive composition in the internal phase is imagewise exposed to actinic radiation. In the most typical embodiments, the photosensitive composition is a photopolymerizable composition including a polyethylene unsaturated compound and a photoinitiator and is encapsulated with a color precursor. Exposure imagewise hardens the internal phase of the microcapsules.
U.S. Pat. No. 4,399,209 discloses a transfer system in which the imaging sheet is assembled with a developer sheet prior to being subjected to a microcapsule rupturing force. Upon passing through pressure rollers in contact with the developer sheet, the microcapsules rupture and imagewise release the internal phase whereupon the color precursor migrates to the developer sheet where it reacts with a dry developer and forms a color image. Imaging systems can be designed to produce monochromatic or polychromatic full color images.
It is often desirable to produce a glossy surface on the developer sheet. Thus, the sheet may include an overcoating of a finely divided thermoplastic developer material. Upon application of heat to this resin material, the resin coalesces, thereby forming a glossy surface for the developer sheet.
Several approaches to heating the glossy material are known. A conductive heating device is disclosed in U.S. Pat. No. 4,761,311, wherein the developer sheet is passed over a curved, heated platen which applies heat to the sheet. In order to effect movement of the sheet, a continuous belt contacts the resin-coated side of the sheet to move it across the platen. One disadvantage with a conductive heating device is that some contact of the resin coating is required. This contact may damage the hot surface of the resin, leaving pick marks or streaking. The apparatus of U.S. Pat. No. 4,761,311 is designed to minimize pressure on the sheet to avoid such problems but does not eliminate the potential problems.
A second approach is through non-contact heating such as by the direction of forced air against the sheet. Such an approach is disclosed, for example, in commonly-assigned, copending U.S. patent application Ser. No. 155,795, filed Feb. 16, 1988. In such a case, heated air is directed against the surface of the sheet. While the use of heated air produce an effectively defect free glossy surface, heating by air is relatively inefficient, thereby requiring long exposure to the heat. This slows the entire image production process.
What is needed, therefore, is a glossing method and apparatus which can be applied to a developer sheet to achieve high throughput times and a defect free glossy surface. At the same time, it is desirable that the method be relatively simple in its practice and that the apparatus be uncomplicated in its construction.